Projector is a display device for producing a large-size screen. The imaging principle of a projector is converting an illumination beam generated by a light source into an image beam by a light valve and projecting the image beam onto a projection screen or a wall through a lens thereby displaying images. With the progress of projection technology and the reduction of manufacturing cost, the application of projector gradually expands from the commercial use to the domestic use, and therefore, the miniature projector having relatively small size and light weight has gradually become the mainstream in the market.
Usually when a projector is use, the size of the projection screen and the distance of the projection screen to the projector may be limited by the environment. Therefore, the lens of the projector usually is disposed with an adjustment ring for adjusting the focal, thereby allowing users to adjust the image projected by the lens through the adjustment ring. A processor in the projector for controlling and driving the lens to move or rotate is required if the lens has an automatic or electrical focal adjustment; and the processor needs to sense and confirm the status of a focal adjustment through a feedback mechanism of a lens movement sensing system before driving the lens to perform the focal adjustment or during the process of the focal adjustment. Lens movement sensing systems can be divided into digital sensing and analog sensing. In the digital sensing, a sensor disposed on the lens is used to issue digital signals to the processor while passing through grating or magnetic grid, and the processor can determine the movement direction and the movement amount according to the number of the grating or magnetic grid has been passed through. In the analog sensing such as potential, resistive, capacitive or photoelectric types, a sensor is used to issue analog signals generated based on the change of voltage or current to the processor while moving, and the processor can determine the movement direction and the movement amount according to the analog signals.
However, the conventional processor has a relatively large size regardless digital sensing or analog sensing is adopted, and the relatively-large processor in size is not conducive to the installation in the miniature projector. Moreover, to work properly, the photoelectric or capacitive sensor must have a calibration each time when the projector is turned on and the installation of the processor inside the projector may lead to the light interference and electrostatic interference. Therefore, it is quite important for the persons in the art to solve the aforementioned problems.
The information disclosed in this “BACKGROUND OF THE INVENTION” section is only for enhancement understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Furthermore, the information disclosed in this “BACKGROUND OF THE INVENTION” section does not mean that one or more problems to be solved by one or more embodiments of the invention were acknowledged by a person of ordinary skill in the art.